Management of cardiac arrhythmia: Tachyarrhythmias

Management of cardiac arrhythmia: Tachyarrhythmias

What causes cardiac arrhythmia?

1. Myocardial factors like ischemia, infarction and myocarditis
2. Autonomic imbalance like sympathetic and parasympathetic overactivity or underactivity
3. Electrolyte imbalance like hypokalemia and hypomagnesemia,
   hypoxia
4. Drugs like antiarrhythmic agents and psychotropic agents
5. Genetic disorders – Channelopathies like Brugada syndrome, long QT syndrome and short QT syndrome

Common supraventricular tachyarrhythmias

1. Atrial fibrillation
2. Atrial flutter
3. AV-nodal reentrant tachycardia
4. Atrioventricular reentrant tachycardia
5. Atrial ectopic tachycardia
6. Preexcitation syndromes combined with atrial fibrillation
7. Multifocal atrial tachycardia

Common ventricular tachyarrhythmias

1. Ventricular tachycardia: monomorphic / polymorphic
2. Ventricular fibrillation

Investigations in a case of cardiac arrhythmia

1. ECG is ideally recorded during the arrhythmia in addition to a routine baseline recording
2. Holter monitoring – used for 24 to 48 hour monitoring with cassette / solid state recorder
3. Loop recorder is an event recorder which monitors continuously and records events
4. Implantable loop recorder can be used for long term recording, upto 18 months
5. Head up tilt test for evaluation of vasovagal syncope
6. Echocardiography to exclude structural heart disease
7. Invasive electrophysiological studies – conventional catheter mapping and programmed stimulation
8. Cardiac mapping using newer modalities like Carto and electroanatomical mapping (3-D mapping)

Therapy of cardiac arrhythmia

Historical aspects

1960s: Bulky pacemakers with limited battery life; Surgery for WPW, VT, SVT
1980s: Catheter ablation – direct current / radiofrequency, ICD
2000s: Refinements in radiofrequency ablation / ICD; newer energy sources like Cryo, Ultrasound

Management of atrial fibrillation

Options in atrial fibrillation are: Rate control with anticoagulation vs rhythm control. Termination can be achieved by synchronized DC Cardioversion. Direct current cardioversion is indicated in atrial fibrillation if there is hemodynamic compromise with hypotension, angina or pulmonary edema. Rate control can be achieved by digoxin, beta blockers or non – dihydropyridine group of calcium channel blockers (verapamil and diltiazem). All these agents can be given orally as well as intravenously depending on the situation. Rhythm control can be achieved by amiodarone, flecainide, quinidine, sotalol or ibutilide.

Anticoagulation has to initiated with heparin and maintained on warfarin with a target INR of 2 – 3 or non-vitamin K oral anticoagulants (NOAC). Long term anticoagulation is decided based on the risk factors using standard scores. Anticoagulation prior to elective cardioversion is given for three weeks if AF has presumably lasted more than 48 hours. Alternate option in case of need for early cardioversion is transesophageal echocardiogram to exclude left atrial thrombus.

Management of atrial flutter

If there is acute hemodynamic collapse or heart failure, emergent synchronized DC Version is needed.

Energies less than 50 J may be sufficient as atrial flutter is highly sensitive to cardioversion, being a macro-reentrant arrhythmia. Atrial / transesophageal pacing may also be able to terminate atrial flutter. Intravenous ibutilide has a 76% success rate. Rate control can be achieved by diltiazem, verapamil, beta blocker or digoxin.

Management of supraventricular tachycardia

Vagal maneuvers like carotid sinus massage or pressure over the eyeballs can be initially tried. In an infant, the dive reflex can be activated by placing ice packs over the face. Adenosine as a bolus injection of 6 -12 mg is very useful in terminating an episode of supraventricular tachycardia. If a second bolus at a higher dose is required, it should not be an add on dose, but a higher dose as the half life of adenosine is very short. Adenosine is contraindicated in asthmatics as it can induce bronchospasm, which can persist upto 30 minutes. Verapamil 5 to 10 mg IV, diltiazem: 0.25 mg/kg over 2 minutes or esmolol: 0.5 mg/kg/min for 1 minute followed by infusion at a rate of 0.05 mg/kg/min for 4 minutes are other options for termination of supraventricular tachycardia.

Management of multifocal atrial tachycardia

Three or more P waves with different morphology at a rate above 100 per minute qualify for a diagnosis of multifocal atrial tachycardia (MAT). ECG of multifocal atrial tachycardia resembles that of atrial fibrillation and flutter. Multifocal atrial tachycardia occurs in seriously ill, elderly individuals, mostly in those with chronic obstructive pulmonary disease. Treatment is that of the underlying condition.

Management of ventricular tachycardia

Lignocaine as 50 – 100 mg intravenous bolus (25 -50 mg/min) followed by 1- 4 mg/min infusion was the sheet anchor of treatment of ventricular tachycardia earlier.

Now amiodarone 150 mg bolus over 10 min followed by an infusion at a rate of 1 mg/ min 6 hrs (360 mg) and 0.5 mg/min 18 hrs (540 mg) is more popular. A word of caution is needed regarding amiodarone infusion. Occasional serious acute pulmonary toxicity can occur and hence the duration of therapy should not exceed 24 to 48 hrs, except when absolutely necessary. Maintenance with oral dosage of amiodarone is necessary for recurrent ventricular tachycardia.

Mexiletine intravenously followed by oral dosage for maintenance is another option.

Ventricular tachycardia with hemodynamic compromise is treated by synchronized direct current cardioversion followed by suppressive therapy as outlined above.

Role of magnesium in the treatment of cardiac arrhythmia

Intravenous magnesium is drug which is often very useful in the management of polymorphic ventricular tachycardia. Deficiency of magnesium is associated with cardiac arrhythmias and can precipitate refractory ventricular fibrillation.

Magnesium deficiency will also hinder replenishment of intracellular potassium as magnesium is a cofactor for the enzyme involved in potassium transport.

1 – 2 g MgSO4 is helpful to suppress life-threatening ventricular tachyarrhythmias and is administered IV over 1 to 2 min. Magnesium is also reported to be useful in digitoxicity.